1. Field of the Invention
The present invention relates to an ultrasonic diagnosis system for producing an ultrasonic image with high positional precision. In the ultrasonic diagnosis system, the periphery of a magnetic sensor in a distal part of an ultrasonic probe, which has an ultrasonic transducer for producing an ultrasonic tomographic image and the magnetic sensor for detecting a position, is made of a non-conductive material in order to reduce an eddy current developing in the periphery of the magnetic sensor and to thus improve the precision in detecting the position of the distal part.
2. Description of the Related Art
In recent years, ultrasonic diagnosis systems for irradiating ultrasonic waves to the inside of a living body, extracting information of an intracorporeal state from echoes, and thus diagnosing a lesion have prevailed widely. Above all, an ultrasonic diagnosis system including an ultrasonic probe for irradiating ultrasonic waves intra-corporeally suffers less decay of ultrasonic waves than a type of ultrasonic diagnosis system that irradiates ultrasonic waves extra-corporeally. High-frequency ultrasonic waves of a high resolution can therefore be employed.
Japanese Unexamined Patent Publication No. 6-261900, describes prior art for detecting the position of an ultrasonic transducer by moving the ultrasonic transducer spirally and utilizing a magnetic field, and constructing a three-dimensional image.
FIG. 1 shows the structure of a prior art distal part 102 of an ultrasonic endoscope 101 serving as an ultrasonic probe. The distal part 102 consists of a distal body 105 attached to the distal end of a casing 104 outlining an insertion unit 103, and a housing 106. An illumination window 107 and objective window 108 are juxtaposed on an inclined surface formed near the center of the distal body 105. A passage hole 110 through which a flexible shaft 109 lies is bored in the distal body 105. The housing 106 communicating with the passage hole 110 is mounted on the distal end of the distal body 105.
A holder 112 having an ultrasonic transducer 111 is located at the distal end of the flexible shaft 109. The ultrasonic transducer 111 is placed in the housing 106. A sealing member 113 for sealing the housing 106 is attached to the proximal end of the holder 112. The housing 106 is filled with an ultrasound propagation fluid (for example, water) 114. A magnetic sensor 115 serving as a position sensor is located at the distal end of the housing 106.
Due to the foregoing structure, the flexible shaft 109 is rotated by a rotation unit that is not shown. This results in radial scanning. Spiral scanning is achieved by advancing or withdrawing the insertion unit 103, that is, advancing or withdrawing the ultrasonic transducer 111. A magnetic field generator is installed extra-corporeally. A magnetic field is detected by the magnetic sensor 115, and sent to a position detector that is an external apparatus. Based on position data computed by involving the position detector, a three-dimensional image is constructed using numerous two-dimensional images resulting from spiral scanning by means of an external apparatus. The image is then displayed on a monitor.
As for the foregoing position sensor-inclusive ultrasonic endoscope, all components thereof including the distal body are made of a conductive material such as a metal. In a magnetic field generated by the magnetic field generator, an eddy current develops on each conductor to consume magnetic energy. This leads to a phenomenon that a magnetic field reaching the magnetic sensor 115 is disordered. Consequently, position detection is not achieved correctly, and a measurement error occurs.